Currently, semiconductor packages are commonly molded with resin in a process referred to as transfer-molding. Resin tablets are heated, melted and compressed, and molten resin is distributed to a plurality of semiconductor devices via a network of runners and gates. The molten resin is then forced into mold cavities where the dies have been placed. Resin is introduced into the cavities of molds through these gates. Traditionally, resin is introduced into the cavities through gates formed in mold halves that are lateral to the surface of the semiconductor device, commonly referred to as a side gate system. However, this has been found to be undesirable because of problems such as wire sweep, that may occur for semiconductor devices having smaller sizes and/or higher pin counts.
Thus, a “direct gating” or “top gating” approach is now gaining popularity, wherein resin is introduced into cavities from gates on top of the semiconductor devices. Amongst other advantages, this approach has been found to avoid the aforesaid problem of wire sweep. An example of its implementation is found in PCT publication number WO 98/50216 entitled “Method and Apparatus for Molding Plastic Packages”. Direct gating generally introduces the use of a removable cavity plate (hereinafter referred to as a “middle plate”) sandwiched between top and bottom halves of a mold to channel and direct resin into the cavities from the top of the cavity. This introduces a new problem of how to efficiently manipulate this extra middle plate.
Since resin travels through the middle plate, it needs to be sufficiently hot to facilitate the flow of molten resin. Otherwise, the resin will harden and set undesirably before the molding process is completed. One solution in the prior art is to pre-heat the middle plate between each molding process by using an external heating apparatus. However, this necessitates transporting the middle plate outside the molding machine to heat up the middle plate, and later to transport it back to the molding press. This requires extra mechanisms to handle the pre-heating process. In addition, a separate de-gating station is required to remove the cull from the molded packages after the molding process is completed.